The nice thing with Dockerfiles and the Docker registry is how quickly I get a reproducible, stateless, isolated environment for any large, proprietary or foreign app I may need, without resorting to a VM or polluting my system. All it takes is an Ubuntu or CentOS base, pull the apps and its dependencies, throw it away when I'm done while keeping a lean Alpine system underneath.
Jails would require me to set things from scratch each time I need a new app, even for a short while. It's just impractical.
I'm considering Nix as a potential alternative, but it doesn't work on the BSDs yet. If you know a way to run "modern workloads" in a KISS, convenient, Unix-y way, please let me know.